SEOUL, South Korea (AP) — The United States and South Korea on Saturday started joint naval exercises that will involve three U.S. aircraft carriers in what military officials describe as a clear warning to North Korea.

The four-day drills that began in waters off South Korea's eastern coast come as President Donald Trump continues a visit to Asia that has been dominated by discussions over the North Korean nuclear threat.

The battle groups of the USS Ronald Reagan, the Theodore Roosevelt and the Nimitz will successively enter the exercise area during the drills that run until Tuesday, South K...